Various methods are known in the art for optical 3D mapping, i.e., generating a 3D profile of the surface of an object by processing an optical image of the object.
Some methods are based on projecting a laser speckle pattern onto the object, and then analyzing an image of the pattern on the object. For example, PCT International Publication WO 2007/043036, whose disclosure is incorporated herein by reference, describes a system and method for object reconstruction in which a coherent light source and a generator of a random speckle pattern projects onto the object a coherent random speckle pattern. An imaging unit detects the light response of the illuminated region and generates image data. Shifts of the pattern in the image of the object relative to a reference image of the pattern are used in real-time reconstruction of a 3D map of the object.
In other methods of optical 3D mapping, different sorts of patterns are projected onto the object to be mapped. For example, PCT International Publication WO 93/03579 describes a three-dimensional vision system in which one or two projectors establish structured light comprising two sets of parallel stripes having different periodicities and angles. As another example, U.S. Pat. No. 6,751,344 describes a method for optically scanning a subject in which the subject is illuminated with a matrix of discrete two-dimensional image objects, such as a grid of dots. Other methods involve projection of a grating pattern, as described, for example, in U.S. Pat. No. 4,802,759. The disclosures of the above-mentioned patents and publications are incorporated herein by reference.
Other methods for 3D mapping and ranging use coded illumination. For example, Sazbon et al. describe a method of this sort for range estimation in “Qualitative Real-Time Range Extraction for Preplanned Scene Partitioning Using Laser Beam Coding,” Pattern Recognition Letters 26 (2005), pages 1772-1781, which is incorporated herein by reference. A phase-only filter codes the laser beam into M different diffraction patterns, corresponding to M different range segments in the workspace. Thus, each plane in the illuminated scene is irradiated with the pattern corresponding to the range of the plane from the light source. A common camera can be used to capture images of the scene, which may then be processed to determine the ranges of objects in the scene.
As another example, PCT International Publication WO 2007/105215 (published after the priority date of the present patent application), whose disclosure is incorporated herein by reference, describes a method for mapping in which a pattern of multiple spots is projected onto an object. The positions of the spots in the pattern are uncorrelated, but the shapes of the spots share a common characteristic. In some embodiments, the spot shape characteristic changes with distance from the illumination source. This distance-varying shape characteristic may be achieved by passing the illumination beam through one or more optical elements that are designed to superpose two optical constraints: one to split the beam into multiple spots, and another to create the distance-varying shape. An image of the spots on the object is captured and processed so as to derive a 3D map of the object.